Mobile communication devices are seemingly everywhere. Indeed, one would be hard-pressed to spend much time in any urban area of the world before seeing people speaking on mobile phones, or being paged, or sending text messages or electronic mail or accessing the Internet using a “personal digital assistant,” or otherwise accessing some form of communications network.
The complicated and coordinated systems that make these communications possible are, however, so generally reliable that most users in highly industrialized countries take their availability for granted. Indeed, most users are made aware of the sophisticated infrastructure behind such systems only on infrequent occasions, for example, when their mobile phone connection is lost in an area of poor coverage, or in boundary zones between cells, or they cannot connect at all because of an unusually high temporary load on the system.
Of course, reality sometimes drastically disrupts such complacency. Disasters, both natural and human-caused, often disable the communications networks many rely on. For example, mobile and fixed telephone systems are often either overloaded or disabled altogether in areas hit by earthquakes, floods, terrorist attacks, etc. Furthermore, other users, such as military personnel in the field, may not have access to the local communications network at all, or may not want to have to rely on vulnerable links to satellite ground stations.
As distressing as system disruption may often be for civilians in affected areas, it often also hinders the ability of emergency personnel to operate most effectively, which may make matters even worse. Aware of this, several companies and authorities have developed both equipment and standards for secondary, often mobile networks that are substantially self-reliant and can be deployed rapidly and are particularly suited for enabling communication between members of a group who need to coordinate work on a common task.
As just one example, in the aftermath of the destruction of New Orleans in the USA in 2005 by Hurricane Katrina, normal access was impossible to primary telecommunications systems such as fixed and mobile telephone services, the Internet, etc. In response, the Sweden-based telecommunications company Ericsson made a transportable, cellular, wireless, voice network system available to various United States authorities to enable voice and data communication between a wide array of disparate agencies operating in New Orleans, including local police, fire-fighters, the Forest Service, and security personnel, to name just a few.
In disaster or other emergency situations, there will usually be some need to prioritize access to the limited resource that such mobile systems represents. For example, each Ericsson system deployed in New Orleans had an operational radius of only about 14 km and could handle fewer than 100 active users at a time. More modern versions have greater range and capacity, but this range and capacity are still much less than, for example, a typical fixed or even mobile telephone network can provide, and some prioritization is still often beneficial or necessary. One example of prioritization might be, in descending order of priority: executive leadership and policy makers; disaster response and military command and control; public health, safety and law enforcement command; public services, utilities and public welfare; and disaster recovery.
Of course, the prioritization scheme—if any is implemented at all—will depend on the situation. Regardless of the scheme, however, in any highly stressful situation, not knowing whom one can or cannot call can have serious or at best undesirable consequences. An additional complication is that, in circumstances such as disasters, in battle zones, etc., the various members of the group who need to communicate with each will often not be known to each other in advance, but to establish communications between two members of the group using mobile telephones, at least the telephone numbers must be known.
Moreover, the roles that persons are carrying out, or their positions in some hierarchy of authority or prioritization, may be as important or even more important than who they are. For example, knowing that a particular mobile phone is associated with a paramedic as opposed to a fire fighter, police officer, search specialist, etc., or with a division commander as opposed to a line officer, will often be more important than knowing their names.
One way to provide the necessary information to the various members of the group would be to have some external information service that could provide contact information to interested parties. Even if it were possible to set up such a service in the event of disruption of established primary networks, however, relaying the retrieved contact information would still cause a delay that might be unacceptable for emergency efforts on the ground. Moreover, in the field of mobile telephony operating according to, for example, the Global System for Mobile (GSM) and Universal Mobile Telecommunications System (UMTS) standards, typically only the priority class of the mobile phone itself is stored in the network in conjunction with its International Mobile Subscriber Identity (IMSI), which is a unique number associated with the network mobile phone users—the IMSI is stored in the Subscriber Identity Module (SIM) in the phone and is transmitted by the phone to the network. This will normally not be enough information for, for example, relevant emergency personnel.